Musty Basement? Humidity, Mold and What Fixes It

A musty smell means moisture, even when there is no puddle. Cool basement walls and floors pick up condensation in humid weather, and damp masonry keeps feeding water into the air.

Measure it. EPA recommends keeping indoor humidity below 60 percent, ideally 30 to 50 percent, and suggests a humidity meter to check. An inexpensive hygrometer tells you whether the basement stays in that range through the summer.

Find the source. White chalky deposits on the wall are efflorescence, a sign of water moving through the masonry. Damp patches at the base of the walls point to seepage that drain tile addresses. A wet window well needs a drain.

Dry the air. A whole-basement dehumidifier with a drain line runs on its own. Fixr puts installation at $1,000 to $2,800.

Mold. EPA says a homeowner can usually clean up an area of less than about 10 square feet; larger growth calls for a remediation provider. Fixr puts remediation at $500 to $1,500 to start and up to $6,000. See basement mold and mildew.

Crawl spaces. A dirt or poorly sealed crawl space can send damp air into the house; encapsulation averages about $5,500 according to This Old House.